PokeCody got it! I mean, he guess like 100 different things, but still!
It's a teleporter, Bills latest invention.
In FRLG, he was working on the prototype, when a clefairy jumped in with him, which combined their molecules in the other machine.
He's finally perfected it.

In order to restrict abuse of the new free machine, you must have visited the city you plan to teleport to.